Fixed point multiplication improvements for AArch64

include/tvm/relay/attrs/transform.h

@@ -298,6 +298,19 @@ struct ClipAttrs : public tvm::AttrsNode<ClipAttrs> {
   }
 };
 
+/*! \brief Attributes for FixedPointMultiply operator */
+struct FixedPointMultiplyAttrs : public tvm::AttrsNode<FixedPointMultiplyAttrs> {
+  int32_t multiplier;
+  int32_t shift;
+
+  TVM_DECLARE_ATTRS(FixedPointMultiplyAttrs, "relay.attrs.FixedPointMultiplyAttrs") {
+    TVM_ATTR_FIELD(multiplier)
+        .describe("Multiplier of a fixed floating point number described as multiplier*2^(shift)");
+    TVM_ATTR_FIELD(shift).describe(
+        "Shift of a fixed floating point number described as multiplier*2^(shift)");
+  }
+};
+
 /*! \brief Attributes for LayoutTransform operator */
 struct LayoutTransformAttrs : public tvm::AttrsNode<LayoutTransformAttrs> {
   std::string src_layout;

include/tvm/tir/builtin.h

@@ -92,6 +92,14 @@ TVM_DLL const Op& shift_right();
  */
 TVM_DLL const Op& large_uint_imm();
 
+/*!
+ * \brief Execute a multiplication between two Q-numbers x and y
+ * followed by a right shift s
+ * The default rounding rule is to the nearest value, rounding half up
+ * (i.e., round(x.1) = x and round (x.5) = x+1)
+ */
+TVM_DLL const Op& q_multiply_shift();
+
 /*!
  * \brief See pesudo code
  *

include/tvm/tir/op.h

@@ -552,6 +552,27 @@ TVM_DLL PrimExpr trunc(PrimExpr x);
  */
 TVM_DLL PrimExpr LargeUIntImm(DataType dtype, int64_t low, int64_t high);
 
+/*!
+ * \brief Execute a multiplication between two Q-numbers x and y
+ * followed by a right shift s. The mathematical expression is:
+ *
+ *    out = round(x*y*2^-s)
+ *
+ * Please note that the two Q-numbers x and y are supposed to have
+ * the same number of fractional bits q.
+ *
+ * More about Q-numbers here: https://en.wikipedia.org/wiki/Q_(number_format)
+ *
+ * The rounding rule is to the nearest value, rounding half up
+ * (i.e., round(x.1) = x and round (x.5) = x+1)
+ * \param x first Q-number
+ * \param y second Q-number
+ * \param q number of fractional bits in x and y. Needs to be > 0
+ * \param s integer right shift
+ * \return The constructed expression.
+ */
+TVM_DLL PrimExpr q_multiply_shift(PrimExpr x, PrimExpr y, PrimExpr q, PrimExpr s);
+
 // Intrinsic operators
 #define TVM_DECLARE_INTRIN_UNARY(OpName)           \
   inline PrimExpr OpName(PrimExpr x) {             \

python/tvm/relay/op/_tensor.py

@@ -131,6 +131,14 @@ def clip_compute(attrs, inputs, output_type):
 
 register_injective_schedule("clip")
 
+# fixed point multiply
+@register_compute("fixed_point_multiply")
+def fixed_point_multiply_compute(attrs, inputs, output_type):
+    assert len(inputs) == 1
+    return [topi.fixed_point_multiply(inputs[0], attrs.multiplier, attrs.shift)]
+
+register_injective_schedule("fixed_point_multiply")
+
 # full
 @script
 def _full_shape_func(shape):

python/tvm/relay/op/tensor.py

@@ -1034,6 +1034,27 @@ def clip(a, a_min, a_max):
     """
     return _make.clip(a, a_min, a_max)
 
+def fixed_point_multiply(data, multiplier, shift):
+    """Fixed point multiplication between data and a fixed point
+    constant expressed as multiplier * 2^(-shift), where multiplier
+    is a Q-number with 31 fractional bits
+
+    Parameters
+    ----------
+    data : relay.Expr
+        The input tensor.
+    multiplier : int
+        The integer multiplier of the fixed point constant.
+    a_max : float
+        The integer shift of the fixed point constant.
+
+    Returns
+    -------
+    result : relay.Expr
+        The output of the fixed point multiplication
+    """
+    return _make.fixed_point_multiply(data, multiplier, shift)
+
 
 def concatenate(data, axis):
     """Concatenate the input tensors along the given axis.

python/tvm/tir/__init__.py

@@ -45,6 +45,7 @@
 from .op import isnan, isfinite, isinf, copysign
 from .op import div, indexdiv, indexmod, truncdiv, truncmod, floordiv, floormod
 from .op import comm_reducer, min, max, sum
+from .op import q_multiply_shift
 
 from . import ir_builder
 from . import transform

python/tvm/tir/op.py

@@ -965,6 +965,34 @@ def popcount(x):
     """
     return call_intrin(x.dtype, "tir.popcount", x)
 
+def q_multiply_shift(x, y, q, s):
+    """Execute a multiplication between two Q-numbers x and y
+    followed by a right shift s. The mathematical expression is:
+
+       out = round(x*y*2^-s)
+
+    More about Q-numbers here: https://en.wikipedia.org/wiki/Q_(number_format)
+    The rounding rule is to the nearest value, rounding half up
+    (i.e., round(x.1) = x and round (x.5) = x+1)
+
+    Parameters
+    ----------
+    x : PrimExpr
+        First Q-number
+    y : PrimExpr
+        Second Q-number
+    q : PrimExpr
+        Number of fractional bits in x and y. Needs to be > 0
+    s : PrimExpr
+        Integer shift
+
+    Returns
+    -------
+    y : PrimExpr
+        The result.
+    """
+    return call_intrin('int32', "tir.q_multiply_shift", x, y, q, s)
+
 def fmod(x, y):
     """Return the remainder of x divided by y with the same sign as x.
 

src/relay/op/tensor/unary.cc

@@ -290,6 +290,29 @@ This function takes a tensor, a minimum value `a_min`, and a maximum value `a_ma
     .set_attrs_type<ClipAttrs>()
     .set_support_level(3);
 
+// relay.fixed_point_multiply
+TVM_REGISTER_NODE_TYPE(FixedPointMultiplyAttrs);
+
+TVM_REGISTER_GLOBAL("relay.op._make.fixed_point_multiply")
+    .set_body_typed([](Expr a, int32_t multiplier, int32_t shift) {
+      auto attrs = make_object<FixedPointMultiplyAttrs>();
+      attrs->multiplier = multiplier;
+      attrs->shift = shift;
+      static const Op& op = Op::Get("fixed_point_multiply");
+      return Call(op, {a}, Attrs(attrs), {});
+    });
+
+RELAY_REGISTER_OP("fixed_point_multiply")
+    .describe(R"code(fixed point multiplication)code" TVM_ADD_FILELINE)
+    .set_num_inputs(1)
+    .add_argument("data", "Tensor", "The input tensor.")
+    .add_type_rel("Identity", IdentityRel)
+    .set_attr<TOpPattern>("TOpPattern", kElemWise)
+    .set_attr<TOpIsStateful>("TOpIsStateful", false)
+    .set_attr<FInferCorrectLayout>("FInferCorrectLayout", ElemwiseArbitraryLayout)
+    .set_attrs_type<FixedPointMultiplyAttrs>()
+    .set_support_level(10);
+
 RELAY_REGISTER_UNARY_OP("floor")
     .describe(R"code(Returns the floor of input array, computed element-wise.
 )code" TVM_ADD_FILELINE)

src/relay/qnn/op/requantize.cc

@@ -153,9 +153,19 @@ Expr RequantizeLower(const Expr& input_tensor, const Expr& input_scale,
         static_cast<double>(input_scale_float) / static_cast<double>(output_scale_float);
     // Skip if input and output scales are same.
     if (!IsEqualScalar(input_scale, output_scale)) {
+      int32_t fixed_point_multiplier, shift;
+      std::tie(fixed_point_multiplier, shift) = GetFixedPointMultiplierShift(double_multiplier);
+
+      const bool is_upward_rounding = (param->rounding == "UPWARD");
+
+      // When using upward rounding (i.e., x.5 rounded to x+1), leverage
+      // the FixedPointMultiply operator
       scaled_int32_t =
-          FixedPointMultiply(scaled_int32_t, double_multiplier, input_shape, param->rounding);
+          (is_upward_rounding
+               ? FixedPointMultiply(scaled_int32_t, fixed_point_multiplier, shift)
+               : FixedPointMultiplyToNearest(scaled_int32_t, double_multiplier, input_shape));
     }
+
   } else {
     // This is per-channel (per=axis) quantization.
     std::vector<double> double_multipliers;

src/relay/qnn/util.cc

@@ -30,25 +30,6 @@ namespace tvm {
 namespace relay {
 namespace qnn {
 
-/*
- * \brief Convert FP32 representation into fixed point representation.
- * \param double_multplier The input FP32 number.
- * \return The pair of multiplier and shift for fixed point representation.
- * \note Converts a floating point number so that it can be represented by
- *       integers. The representation is
- *             float_number = (significand) * 2^(exponent)
- *
- *       The significand is a number between 0.5 and 1. This is represented by
- *       an integer number. For example, if it is int32, then the decimal point
- *       exists between bit 31 and 30 from LSB (or between first and second bit
- *       from the left).
- *
- *       Some examples are
- *           0.25 = (0.5) * 2^(-1)
- *           0.125 = (0.5) * 2^(-2)
- *
- *       Credit to TFLite reference implementation.
- */
 std::pair<int32_t, int32_t> GetFixedPointMultiplierShift(double double_multiplier) {
   int32_t significand, exponent;
   if (double_multiplier == 0.) {
@@ -75,8 +56,8 @@ std::pair<int32_t, int32_t> GetFixedPointMultiplierShift(double double_multiplie
   return std::make_pair(significand, exponent);
 }
 
-Expr FixedPointMultiply(Expr tensor, double multiplier, const Array<IndexExpr>& input_shape,
-                        const std::string& rounding) {
+Expr FixedPointMultiplyToNearest(Expr tensor, double multiplier,
+                                 const Array<IndexExpr>& input_shape) {
   // Choose high precision datatype to be int64. This is for avoiding overflow
   // in multiplication of two int32 values.
   DataType hp_dtype = DataType::Int(64);
@@ -109,19 +90,15 @@ Expr FixedPointMultiply(Expr tensor, double multiplier, const Array<IndexExpr>&
   int64_t pos_rounding_value = (1ll << (total_right_shift - 1));
 
   Expr round_scalar;
-  if (rounding == "UPWARD") {
-    round_scalar = MakeConstantScalar(hp_dtype, pos_rounding_value);
-  } else if (rounding == "TONEAREST") {
-    auto pos_rounder = MakeConstantScalar(hp_dtype, pos_rounding_value);
-    auto neg_rounder = MakeConstantScalar(hp_dtype, pos_rounding_value - 1);
-    auto pos_rounder_t = Full(pos_rounder, input_shape, hp_dtype);
-    auto neg_rounder_t = Full(neg_rounder, input_shape, hp_dtype);
 
-    auto zero_t = Zeros(input_shape, hp_dtype);
-    round_scalar = Where(GreaterEqual(tensor, zero_t), pos_rounder_t, neg_rounder_t);
-  } else {
-    LOG(FATAL) << "Rounding mode " << rounding << " not supported.";
-  }
+  auto pos_rounder = MakeConstantScalar(hp_dtype, pos_rounding_value);
+  auto neg_rounder = MakeConstantScalar(hp_dtype, pos_rounding_value - 1);
+  auto pos_rounder_t = Full(pos_rounder, input_shape, hp_dtype);
+  auto neg_rounder_t = Full(neg_rounder, input_shape, hp_dtype);
+
+  auto zero_t = Zeros(input_shape, hp_dtype);
+  round_scalar = Where(GreaterEqual(tensor, zero_t), pos_rounder_t, neg_rounder_t);
+
   // Add the rounding scalar.
   tensor = Add(tensor, round_scalar);
 

src/relay/qnn/util.h

@@ -70,6 +70,27 @@ static inline int32_t GetQmax(const DataType& dtype) {
   }
 }
 
+/*
+ * \brief Convert FP32 representation into fixed point representation.
+ * \param double_multplier The input FP32 number.
+ * \return The pair of multiplier and shift for fixed point representation.
+ * \note Converts a floating point number so that it can be represented by
+ *       integers. The representation is
+ *             float_number = (significand) * 2^(exponent)
+ *
+ *       The significand is a number between 0.5 and 1. This is represented by
+ *       an integer number. For example, if it is int32, then the decimal point
+ *       exists between bit 31 and 30 from LSB (or between first and second bit
+ *       from the left).
+ *
+ *       Some examples are
+ *           0.25 = (0.5) * 2^(-1)
+ *           0.125 = (0.5) * 2^(-2)
+ *
+ *       Credit to TFLite reference implementation.
+ */
+std::pair<int32_t, int32_t> GetFixedPointMultiplierShift(double double_multiplier);
+
 Expr RequantizeLower(const Expr& input_tensor, const Expr& input_scale,
                      const Expr& input_zero_point, const Expr& output_scale,
                      const Expr& output_zero_point, const RequantizeAttrs* param,
@@ -94,13 +115,12 @@ static inline int64_t get_const_int(const tvm::PrimExpr& x) {
 
 /*
  * \brief Fixed point multiplication between integer tensor with floating point
- scalar.
+ * scalar. This implementation rounds  to the nearest value when it is midway
+ * between two representable values.
  * \param tensor The quantized input tensor of dtype int64.
  * \param multiplier The scalar multiplier.
  * \param input_shape Shape of the input tensor.
- * \param rounding "UPWARD" or "TONEAREST". The rounding direction when the value
- is midway between" "two representable values.
- * \return The sequence of Relay ops for fixed point multiplication.
+ * \return The sequence of Relay ops for fixed point multiplication with TONEARES rounding.
 
  * \note Original compuation is scale_fp32 * quantized_tensor.  To convert into
  *       integer computation, the multiplication with fp32 scalar can be
@@ -114,8 +134,8 @@ static inline int64_t get_const_int(const tvm::PrimExpr& x) {
  *       2) Round the result.
  *       3) Right shift the result
  */
-Expr FixedPointMultiply(Expr tensor, double multiplier, const Array<IndexExpr>& input_shape,
-                        const std::string& rounding);
+Expr FixedPointMultiplyToNearest(Expr tensor, double multiplier,
+                                 const Array<IndexExpr>& input_shape);
 
 /*
  * \brief Fixed point multiplication between integer tensor with floating point

src/relay/quantize/realize.cc

@@ -113,7 +113,14 @@ inline Expr MulAndDiv(Expr data, float s1, float s2, DataType dtype,
   } else if (static_cast<int>(factor) == factor) {
     return Multiply(data, MakeConstantScalar(dtype, factor));
   } else {
-    data = qnn::FixedPointMultiply(data, factor, data_shape, cfg->rounding);
+    if (cfg->rounding == "UPWARD") {
+      int32_t fixed_point_multiplier, shift;
+      std::tie(fixed_point_multiplier, shift) = qnn::GetFixedPointMultiplierShift(factor);
+      data = relay::FixedPointMultiply(data, fixed_point_multiplier, shift);
+    } else {
+      data = qnn::FixedPointMultiplyToNearest(data, factor, data_shape);
+    }
+
     return Cast(data, dtype);
   }
 }
@@ -164,8 +171,15 @@ Expr QuantizeRealize(const Call& ref_call, const Array<Expr>& new_args, const Ob
       return QRealizeIntExpr(data, dom_scale, n->dtype);
     } else {
       data = Cast(data, DataType::Int(64));
-      data = qnn::FixedPointMultiply(data, idom_scale_imm / odom_scale_imm,
-                                     ref_call->type_as<TensorTypeNode>()->shape, cfg->rounding);
+      if (cfg->rounding == "UPWARD") {
+        int32_t fixed_point_multiplier, shift;
+        std::tie(fixed_point_multiplier, shift) =
+            qnn::GetFixedPointMultiplierShift(idom_scale_imm / odom_scale_imm);
+        data = relay::FixedPointMultiply(data, fixed_point_multiplier, shift);
+      } else {
+        data = qnn::FixedPointMultiplyToNearest(data, idom_scale_imm / odom_scale_imm,
+                                                ref_call->type_as<TensorTypeNode>()->shape);
+      }
       data = Cast(Clip(data, clip_min_imm, clip_max_imm), n->dtype);
       return QRealizeIntExpr(data, dom_scale, n->dtype);
     }

src/relay/transforms/pattern_util.h

@@ -495,6 +495,14 @@ inline Expr Round(Expr x) {
 
 inline Expr Clip(Expr x, double a_min, double a_max) { return MakeClip(x, a_min, a_max); }
 
+inline Expr FixedPointMultiply(Expr x, int32_t multiplier, int32_t shift) {
+  static const Op& op = Op::Get("fixed_point_multiply");
+  auto attrs = make_object<FixedPointMultiplyAttrs>();
+  attrs->multiplier = multiplier;
+  attrs->shift = shift;
+  return Call(op, {x}, Attrs(attrs), {});
+}
+
 inline Expr Add(Expr lhs, Expr rhs) {
   static const Op& op = Op::Get("add");
   return Call(op, {lhs, rhs}, Attrs(), {});